Thermoelectric cooling device for heat conductive light transparent surfaces



y 7, 1964 s. E. MAYER ETAL 3,139,733

THERMOELECTRIC COOLING DEVICE FOR HEAT CONDUCTIVE LIGHT TRANSPARENTSURFACES Filed Jan. 15, 1962 2 Sheets-Sheet 1 FIG. I

SIMON E. MEE

IANHRITCHIE BY ABRAHAM I. MLAVSKY WW W*W ATTORNEYS July 7, 1 s. E. MAYERETAL THERMOE-LECTRIC COOLING DEVICE FOR HEA CONDUCTIVE LIGHT TRANSPARENTSURFACES 2 Sheets-Sheet 2 Filed Jan. 15, 1962 FIG. 3

FIG. 4

INVENTORS SIMON E. MAYER IAN MRITCHIE BY ABRAHAM l. M WMWY LAVSKYATTORNEYS United States Patent THERMOELECTRIC COOLING DEVICE FOR HEATCONDUCTIVE LIGHT TRANSPARENT SURFACES Simon E. Mayer, Lexington, Ian M.Ritchie, Wakefield,

and Abraham I. Mlavsky, Belmont, Mass, assignors t0 TransitronElectronic Corporation, Wakefield, Mass.

Filed Jan. 15, 1962, Ser. No. 166,300 Claims. (Cl. 62-3) The presentinvention relates to a means for thermally controlling an energyresponsive surface with minimum interference of the impingement ofenergy on said surface.

There are several applications where it is desirable to provide a meansfor eifectively controlling the temperature of a surface whilesimultaneously allowing certain forms of energy to impinge upon thesurface. For example, it is desirable to provide a means for cooling aphotomultiplier tube surface without interfering with light impingingupon the tube. Similarly, it is desirable under certain circumstances tocontrol the temperature of infrared cells without interfering with theimpingement of infrared rays upon the cell.

It is therefore, an object of the present invention to provide a compactand relatively simple device for thermally controlling a surface of anobject, such as a photomultiplier tube or infrared cell withoutinterfering with the pasage of energy in wave form onto the surface.

The problem of cooling photomultiplier tubes is particularly acute.Heretofore, various methods of cooling have been attempted. A commonmethod has been to place the photomultiplier tube and associatedmechanism in a commercial type of freezer. Such an arrangement isunsatisfactory because parts of the apparatus which operate best aboveroom temperature are cooled with the tube. In addition, the arrangementis clumsy. More recently, Kolenko, Protopopov, Fleyshman and Yuryev havetaught that photomultiplier tubes may be cooled with the aid ofthermoelectric coolers. (Electronic Design, October 28, 1959.) Thearrangement as described therein, however, is inadequate as it severelyobstructs the passage of light to the photomultiplier tube, and does notpermit replacement of the photomultiplier tube separately from thecooling device.

It is, therefore, an object of the present invention to provide a meansfor cooling a photomultiplier tube wherein the face of the photocathodeis not obstructed. Heat is also abstracted in a relatively uniformmanner from the entire surface of the photocathode without lateralconduction of heat across the thin glass face of the photocathode.Photomultiplier tubes may be replaced without simultaneous replacementof the cooling mechanism. It is also an object of the present inventionto provide a means for cooling the surface of a photomultiplier tube toapproximately 10 C. whereby thermal noises of the tube may be reduced bya factor of at least 5.

In the present invention there is provided an arrangement wherein aheat-conductive light-transparent sheet is supported by a primary heatconductive ring extending about the periphery of the sheet. A secondaryring comprising an annular tubular member through which a heatable fluidmedium such as water may be circulated is positioned in spaced coaxialrelation with the primary ring. Disposed between the rings are aplurality of thermoelectric couples or elements, preferably connected inelectrical series. Each thermoelectric element has a hot and a cold end.The cold ends are in thermal engagement with the primary ring while thehot ends are in thermal engagement with the secondary ring. Thesecondary ring acts as a heat sink for the thermoelectric elements andis connected thermally to each thermoelectric element by means of rodswhich support the thermoelectric element "ice at one end and which atthe other are secured in a hole in the secondary ring, with suitablemeans for providing a thermal contact.

These and other objects and advantages of the present invention will bemore clearly understood when considered in conjunction with theaccompanying drawings in which:

FIG. 1 is a schematic view of an embodiment of the present invention foruse in conjunction with a photomultiplier tube,

FIG. 2 is a schematically illustrated detail of the present invention,

FIG. 3 is a plan view of a preferred embodiment of the presentinvention, and,

FIG. 4 is a cross sectional view of the embodiment illustrated in FIG. 3taken along the line 44 of FIG. 3.

The present invention may be used in connection with a variety ofdevices wherein it is desirable to control the temperature of a surfaceof the device without obstructing the impingement of energy, primarilyin the form of light, onto the surface of the device. The principalutility of the present invention, however, is for coolingphotomultiplier tubes. Accordingly, the present invention will bedescribed in connection with an embodiment of the invention for suchpurpose.

Photomultiplier tubes such as illustrated at 1 in FIG. I normallyoperate more reliably when the photomultiplier dark current is reduced.This dark current may be reduced considerably by supressing thermionicemission from the cathode. In addition, cooling 2. photomultiplier tubenoticeably reduces leakage current.

The device illustrated generally at 3 (FIG. 1) has a light-transparentheat-conductive sheet 4 with a flat surface 5 adapted to be positionedin parallel face to face contact with the flat surface 6 at the cathodeend of the tube 2. For photomultiplier tube coolers, the sheet 4preferably should be of glass having an index of refractionsubstantially equal to the index of refraction of the glass envelope ofthe photomultiplier tube. By equating the index of refraction, loss oflight transmission due to internal reflections at the interface of thesheet 4 and surface 6 is minimized. A common index of refraction forsuch tubes is 1.5000.

To further minimize the internal reflection at the interface of thesheet 4 and surface 6, a thin layer of oil 7 may be spread between thetube 1 and sheet 4. Such oil must not freeze or be voltaile at roomtemperatures. It must have the same index of refraction or close to thesame index or refraction as the transparent sheet 4. It must betransparent and must not act as a substantial heat barrier. It has beenfound that various silicon oils are satisfactory for such purpose.

The sheet 4 is preferably a disc of substantially the same diameter asthe photomultiplier tube. (FIGS. 3 and 4.) It is supported at itsperiphery by a primary ring 8 of heat conductive material such, forexample, as aluminum. This ring 3 may be formed in two sectionsincluding the base rim 9 having an annular cross section as illustratedin FIG. 4 and a clamping ring 10. The sheet 4 is sandwiched between thebase rim 9 and clamping ring 10 with a the base rim 9 and clamping ring10 suitably secured together by solder or other suitable means. Theouter edge of the ring 8 is polyhedric in shape and, as illustrated inFIG. 3, may have an octagonal configuration with sides illustrated at11.

A secondary ring 12 is positioned coaxial with and surrounding theprimary ring 8. This secondary ring 12 is maintained in spaced relationwith the primary by a series of radially extending braces 13interengaging the primary and secondary rings. The secondary ringcomprises a tubular member having walls 14, 15, 16 and 17 forming apassage 18 through which a heat exchange fluid medium may pass. Inletand outlet connections 19 and 20 are connected to the passage 18 so thatwater may be pumped into the inlet 19 and drained from the passage 18 atthe outlet 20. A plurality of thermoelectric couples 21, 22, 23, 24, 25,26, 27 and 28'are arranged in electrical series, and are disposedbetween the primary and secondary rings 8 and 12 respectively. Eachthermoelectric couple is identical in construction and hasthermoelectric positive and negative members such as illustratedrespectively at 21 and 21b. These members 21a and 21b are interconnectedby a silver plated copper connecting strap 29. This strap 29 iselectrically and thermally conductive and is secured in face to facerelation with one of the octagonal sides of the ring 8. These straps 29also form the'cold junction of the thermoelectric couple. Adjacentthermoelectric couples are connected in series by a connecting copperweb 3%) with the web 30 secured at its ends to end caps 31 and 32. Thecaps 31 and 32 are soldered or otherwise suitably secured to the hotends of thermoelectric members. The copper end caps are also eachsecured to a thermally conductive rod or plunger 34 with the rod orplunger 34 electrically insulated from the caps 31 and 32. (FIG. 2.) Therod 34 is preferably secured to the caps 31, 32 by a thin layer of anelectrically insulating, but thermally conductive glue 38. Such gluemust provide a solid interengagement between the cap and rod and maycomprise a wide range of resin glues. Epoxy glues are preferred. Therods 34 each slideably fit a hole 35 formed in the secondary ring 12.The rod 34 and walls of the hole 35 have a relatively tight sliding fitso that a good thermally conducting interface is formed between each rod34 and ring 12. The rod 34 is preferably an anodized aluminum memberwith a relatively electrically nonconductive surface.

A thermally conductive wad 36 of metal wool made of aluminum, copper orother similar metals is packed in the hole 35 in thermal and pressurecontact with the secondary ring 12 and rod 34. The wool is securedwithin the hole 35 by the pointed plug 37 which is threaded into theouter end of the hole 35. Such an arrangementperrnits good thermalconductivity between the ring 12 and rod 34 while maintaining a veryhigh electrical resistance and providing expansion compensation.

' What is claimed is:

1. means for conducting heat from an electron emissive glass surfacecomprising a heat-conductive lighttransparent glass sheet having oneside parallel and closely spaced in thermal contact with said surface,

a thin layer of an optically and thermally conductive materialinterposed between and contiguous with said surface and side,

and means at the periphery of said sheet for conducting heat therefrom,

said means comprising a first heat conductive ring surrounding and inclamping engagement with said glass sheet and a plurality ofthermoelectric devices thermally connected to said ring.

2. A means for controlling temperature on a surface while said surfaceis illuminated comprising a heat-conductive light-transparent sheetadapted to be positioned with a side thermally contacting said surface,

heat-conductive means arranged about the periphery of said sheetsupporting said sheet in clamping engagement and,

thermoelectric means arranged about the periphery of saidheat-conductive means and in direct thermal and electrical contacttherewith, for cooling said heat conductive means,

and means in slidable contact with and arranged about the periphery ofsaid'thermoelectric meansfor conducting heat from said thermoelectricmeans.

3. A means for controlling heat on a surface while said surface isilluminated comprising a heat-conductive lighttransparent sheet havingan index of refraction substantially equal to the index of refraction ofsaid sheet adapted to be positioned with a side thermally contactingsaid surface, a

primary and secondary concentric rings,

said primary ring comprising a metallic thermally conductive memberengaging said surface,

said secondary ring comprising an annular tubular member through which aheat exchanging fluid may be circulated for establishing a predeterminedtemperature level of said secondary ring,

a plurality of thermoelectric elements arranged radially about saidsheet and each having a cold and hot end with said cold ends disposedagainst said metallic ring in electrical contact therewith and said hotends disposed against the other of said rings. I a

4. A means for controlling heat on a surface while said surface isilluminated comprising a heat-conductive lighttransparent sheet adaptedto be positioned with a side thermally contacting said surface,

primary and secondary concentric rings,

said primary ring comprising a thermally conductive member engaging saidsurface,

said secondary ring comprising an annular tubular member through which aheat exchanging fluid may be circulated for establishing a predeterminedtemperature level of said secondary ring,

a plurality of thermoelectric elements arranged radially about saidsheet and having hot and cold ends,

said hot ends thermally engaging said secondary ring through a highelectrical resistance joint and said cold ends thermally engaging saidprimary ring in electrical contact therewith.

5. A device asset forth in claim 4 having means forming a plurality ofradially extending holes formed in said tubular member,

a plurality of rods secured at one end in one of said holes,

and means supporting and thermally interengaging and electricallyinsulating the other end of each of said rods and a thermoelectricelement.

6. A device asset forth. in claim 5 having metallic wool positioned insaid holes thermally interengaging said rod and said means forming saidhole. 7

7. A device for conducting heat from the electrom emissive surface of aphotomultiplier tube or the like comprising a heat-conductivelight-transparent sheet, 7 1

a metallic heat conductive ring positioned about in clampingengagementtherewith and supporting said sheet, 7

a second tubular ring having a passage therethrough for circulating afluid coolant,

a plurality of thermoelectric elements radially disposed about saidsheet with each having one end thermally engaging said first mentionedring and another end thermally engaging said second ring in slidingcontact therewith through a high electrical resistance joint,

said thermoelectric elements adapted to respond to a power input to makesaid first end cooler than said second end.

8. A device as set forth in claim 7 wherein said sheet is glass.

9. A device as set forth in claim 7 wherein said sheet is quartz.

10. A device as set forth in claim 7 wherein said sheet is transparentto infrared rays.

References Cited in the file of this patent UNITED STATES PATENTS WallerNOV. 20, 1962

1. A MEANS FOR CONDUCTING HEAT FROM AN ELECTRON EMISSIVE GLASS SURFACECOMPRISING A HEAT-CONDUCTIVE LIGHTTRANSPARENT GLASS SHEET HAVING ONESIDE PARALLEL AND CLOSELY SPACED IN THERMAL CONTACT WITH SAID SURFACE, ATHIN LAYER OF AN OPTICALLY AND THERMALLY CONDUCTIVE MATERIAL INTERPOSEDBETWEEN AND CONTIGUOUS WITH SAID SURFACE AND SIDE, AND MEANS AT THEPERIPHERY OF SAID SHEET FOR CONDUCTING HEAT THEREFROM, SAID MEANSCOMPRISING A FIRST HEAT CONDUCTIVE RING SURROUNDING AND IN CLAMPINGENGAGEMENT WITH SAID GLASS SHEET AND A PLURALITY OF THERMOELECTRICDEVICES THERMALLY CONNECTED TO SAID RING.